1910.] FROM MERGUI ARCniPELAGO. 811 



Thyroscyphus regularis Jaflei-liolni, 1S96. (Plate LXXVII. 



fig. 7.) ; 



{T. cequalis Wurreii, 1908.) 



Trop]iosome. The specimens are somewhat larger than those 

 originally describeiT, sometimes almost 20 cm. in length, while the 

 branches may reach a length of 45 mm., in place of the maximum 

 of 18 mm. given by Jaderholm. 



The species is readily distinguished from T. vitieiisis by the 

 presence of a very distinct ojjerculum. accompanied by deep bays 

 round the margin ; further, the bright rim runs in this case 

 much nearer to the edge, and is not so pronounced, while the faint 

 ringing at the internodes is more marked. The joints, varving 

 in number, which are said to occur on the peduncle, are only 

 occasionally present (though sometimes up to three or four were 

 observed), and even then they are not essential to the specific 

 structure, for they are due to the desti'uction of the hydrotheca, 

 and to the subsec|uent regeneration of a new hydrotheca from 

 within the remains of the old one, the apparent joints being the 

 reliquiae of former calycles. No specific value can attach to 

 these accidental " joints," the like of which I have already 

 observed in Thyroscy2yhus simj^lex = iridentatus (1909, p. 75, 

 fig. 1 b) and in Lytosci/phus marginatus ; but in T. ramosus the 

 semblance of a twist occurs in the peduncle. 



The minute structure of the coenosarc is obscured by the 

 presence of opaque granules which occur in great abundance. In 

 these specimens the hydranth is attached, not to a continuous 

 ridge, as in the specimens from ]Sra.tal, wliich Warren has de- 

 scribed as T. requalis (and which I am unable to distinguish from 

 T. reijidaris), but to a row of small chitinous prominences which 

 I'uns round the inside of the hydrotheca in an exceedingly 

 sinuous curve, having two maxima, one on the adcauline, the 

 other on the abcauline surface, and two lateral minima. 



Gonosome. Gonangia, which have not previously been described, 

 were found on a single colony from Station 25 (PI. LXXVII. 

 fig. 7). The coenosarc has disappeared, but the perisarc is in the 

 form of a long cylinder, larger even than that of T. torresii (see 

 Jaderholm, 1903, p. 273). V^ry indefinite and irregular wrinkles 

 appear on the perisarc. The insignificant stalk of the gonangium 

 arises from the projection of the internode upon which a hvdro- 

 theca is j^jerched 



Dimensions : — 



Branch, diameter 0"36 mm. 



Distance between hydrothecoe 1"13 to 1 -3 mm. 



Hydrotheca, depth 0-96 mm. 



,, breadth at mouth 0-63 mm. 



Peduncle, diameter 0*20 mm. 



Gonangium, length 3 mm. 



,, breadth 1mm. 



Localities. A large bunch of colonies from 8t. 22, Hastings 



